As I was biking to school this morning, I saw one of my professors walking in the same direction. I slowed down and said hello, then continued on my way. In order to regain the lost speed, I pedaled harder. Unfortunately, my left foot slipped when it was in the front. This caused the pressure of a fast pedaling in the right foot to continue downward, only this time in the opposite direction. Since there are no gears for biking backwards, it went much faster than it would for going forward. And combining this with the fact that my left foot was no longer on the pedal, it resulted in a pedal going very quickly into my left shin.
It hurt. A lot. Still does.